Radiant fuser for xerographic reproducing apparatus

ABSTRACT

Apparatus for heat fixing toner images electrostatically adhered to copy paper. The apparatus is characterized by the provision of plural radiant energy sources capable of fusing low density as well as high density images in an efficient manner. In order to prevent physical contact of the radiant energy sources by the copy paper, a shield is provided which is transparent to energy in the wave length bands required for fusing high and low density images.

United States Patent Thettu 1 Aug. 5, 1975 [5 1 RADIANT FUSER FORXEROGRAPHIC 3,452,181 6/1969 Stryjewski 219/388 x REPRODUCING APPARATUS3,795,787 3/1974 Nogaito 219/216 3,811,828 5/1974 Ohta 219/216 X [75]Inventor: Raghulinga R. Thettu, Webster,

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Feb. 25, 1974 [21] Appl. No: 446,192

[52] [1.8. CI. 219/216; 219/347; 219/350; 219/354; 219/388 [51] Int. Cl.H05b 1/00; 603g 15/20 [58] Field of Search 219/216, 388, 347, 350,219/352, 354; 432/60, 228; 118/637; l17/l7.5; 355/9, 17

[56] References Cited UNITED STATES PATENTS 3,449,546 6/1969 Dhoble219/216 Prinmry E.\'aminer=C. L. Albritton [57] ABSTRACT Apparatus forheat fixing toner images electrostatically adhered to copy paper. Theapparatus is characterized by the provision of plural radiant energysources capable of fusing low density as well as high density images inan efficient manner. In order to prevent physical contact of the radiantenergy sources by the copy paper, a shield is provided which istransparent to energy in the wave length bands required for fusing highand low density images.

4 Claims, 4 Drawing Figures PATENTED Aug 5|975 3,898,424

SHEET 1 PATENTEWB 3,898,424

SHEET RADIANT FUSER FOR XEROGRAPIIIC REPRODUCING APPARATUS BACKGROUND OFTHE INVENTION This invention relates generally to electrostatographiccopying apparatus and, more particularly, to radiant energy apparatusfor fixing toner images to a support member.

In the process of electrostatography, latent electrostatic images areformed on a support member, for example, plain paper with the subsequentrendering of the latent images visible by the application ofelectroscopic marking particles, commonly referred to as toner. Thetoner or powder images so formed vary in density in accordance with themagnitude of electrostatic charges forming the individual images. Thetoner images can be fixed directly upon the support member on which theyare formed or they may be transferred to another support member withsubsequent fixing of the images thereto.

Fixing of toner images can be accomplished by various methods one ofwhich is by the employment of thermal energy. In order to permanentlyfix or fuse toner images onto a support member by means of thermalenergy it is necessary to elevate the temperature of the toner materialto a point at which the constituents of the toner coalesce and becometacky or melt. This action causes the toner to be absorbed to someextent into the fibers of the paper. Thereafter as the toner cools,solidification of the toner material occurs causing it to be firmlybonded to the support member. In the process of electrostatography, theuse of thermal energy for fixing toner images is old and well known.

One approach to thermal fusing of toner images onto a support member isto pass the support with the toner images thereon past a source ofradiant energy such that the image bearing side of the support isopposite the source of radiation while the reverse side thereof is movedin contact with a heated platen. In the foregoing arrangement, forreasons understood by those skilled in the art, the radiant energysource is so constructed and functions such that it radiates energy atshort wave lengths (i.e., 0.5-2.0 microns) which satisfactorily fuseshigh density images by means of the energy being directly absorbed bythe toner. The heated platen provides thermal energy for elevating thetemperature of the copy paper so that the paper does not act as a heatsink which would rob the toner images of heat provided by the radiantsource. While the foregoing arrangement has been found to operatesatisfactorily, it is possible for the low density images not to befused satisfactorily due to either, the lack of intimate contact betweenthe reverse side of the paper and the platen or the platen not being atthe proper fusing temperature when the copy paper passes thereover.Moreover, in a duplex mode of operation the heated platen which operatesabove the softening point of the toner causes offsetting of toner to theplaten.

Accordingly, it is the primary object of this invention to provide a newand improved electrostatographic apparatus.

It is a more particular object of this invention to provide a new andimproved radiant fuser for use in a xerographic reproducing apparatus.

Another object of this invention is to provide, in a radiant fuser, ashield disposed between the radiant energy source and image supportmember which shield is transparent to substantially all the energyemitted from the source whereby high and low density images are fused byradiant energy.

BRIEF SUMMARY OF THE INVENTION Briefly, the above-cited objects areaccomplished by the provision of a radiant fuser having two sources ofradiant energy. The peak power of one of the sources is concentrated atwave lengths on the order of 0.5-2.0 microns while the peak power of theother is concentrated at wave lengths greater than 2 microns.

In order to prevent physical contacting of the radiant energy sources bythe copy paper, a shield is supported intermediate the source and thecopy paper. The shield, unlike prior art devices is transparent tosubstantially all energy wave lengths emitted from the sources.

In one embodiment of the invention the radiation sources comprise aquartz lamp which emits the short wave length energy and a reflectorwhich absorbs energy emitted from the quartz lamp and re-radiates longwave length energy for heating the copy paper to thereby fuse the lowerdensity images. As will be appreciated, the short wave length energy isdirectly absorbed by the toner images having a high density of tonerparticles.

In another embodiment of the invention, a resistance heater operating ata much lower surface temperature than the quartz lamp it is substitutedfor the reflector.

Other objects and advantages of the invention will become apparent inview of the detailed description to follow when read in conjunction withthe accompanying drawings wherein:

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of areproducing apparatus incorporating the invention;

FIG. 2 illustrates a sectional view in elevation of a radiant fuserincorporated in the apparatus of FIG. 1;

FIG. 3 illustrates a modified embodiment of the radiant fuserillustrated in FIG. 2; and

FIG. 4 is a perspective view of a shield and support thereforeincorporated in the fuser of FIGS. 2 and 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG.1, there is shown by way of example an automatic xerographic reproducingmachine 1 which incorporates the improved fusing apparatus 15 of thepresent invention. The reproducing machine 1 depicted in FIG. 1illustrates the various components utilized therein for producing copiesfrom an original. Although the fusing apparatus 15 of the presentinvention is particularly well adapted for use in an automaticxerographic reproducing machine I, it should become evident from thefollowing description that it is equally well suited for use in a widevariety of machines where an image is fused to a sheet of final supportmaterial and it is not necessarily limited in its application to theparticular embodiment shown herein.

The reproducing machine 1 illustrated in FIG. 1 employs an imagerecording drum-like member 10 the outer periphery of which is coatedwith a suitable photoconductive material 11. One type of suitablephotoconductive material is disclosed in US. Pat. No. 2,970,906 issuedto Bixby in 1961. The drum 10 is suitably journaled for rotation withina. machine frame (not shown) by means of a shaft 12 and rotates in thedirection indicated by arrow 13, to bring the image retaining surfacethereon past a plurality of xerographic processing stations. Suitabledrive means (not shown) are provided to power and coordinate the motionof the various cooperating machine components whereby a faithfulreproduction of the original input scene information is recorded upon asheet 14 of final support material such as paper or the like.

Since the practice of xerography is well-known in the art, the variousprocessing stations for producing a copy of an original arehere'lLrepresented in FIG. I as blocks A to E. Initially, the drum 10moves photoconductive surface 11 through charging station A. At chargingstation A an electrostatic charge is placed uniformly over thephotoconductive surface 11 of the drum 10 preparatory to imaging. Thecharging may be provided by a corona generating device of a typedescribed in U.S. Pat. No. 2,836,725 issued to Vyverberg in 1958.

Thereafter, the drum 10 is rotated to exposure station B where thecharged photoconductive surface 11 is exposed to a light image of theoriginal input scene information, whereby the charge is selectivelydissipated in the light exposed regions to record the original inputscene in the form of a latent electrostatic image. A suitable exposuresystem may be of the type described in U.S. patent application Ser. No.259,181 filed June 2, 1972.

After exposure, drum 10 rotates the electrostatic latent image recordedon the photoconductive surface 11 to development station C wherein aconventional developer mix is applied to the photoconductive surface 11of the drum l rendering the latent image visible. A suitable developmentstation is disclosed in U.S. patent application Ser. No. 199,481 filedNov. 17, 1971. The application describes a magnetic brush developmentsystem utilizing magnetizable developer mix having carrier granules andtoner colorant. The developer mix is continuously brought through adirectional flux field to form a brush thereof. The electrostatic latentimage recorded on photoconductive surface 11 is developed by bringingthe brush of developer mix into contact therewith.

The developed image on the photoconductive surface II is then broughtinto contact with a sheet 14 of final support material within a transferstation D and the toner image is transferred from the photoconductivesurface 11 to the contacting side of the final support sheet 14. Thefinal support material may be paper, plastic, etc., as desired. Afterthe toner image has been transferred to the sheet of final supportmaterial 14, the sheet with the image thereon is advanced to a fuserassembly 15, which fixes the transferred powdered image thereto. Afterthe fusing process, the sheet 14 is advanced through a snuffingapparatus 2 then by rolls 16 to a catch tray 17 for subsequent removaltherefrom by the machine operator.

Although a preponderence of the toner powder is transferred to the finalsupport material 14, invariably some residual toner remains on thephotoconductive surface 1 1 after the transfer of the toner powder imageto the final support material 14. The residual toner particles remainingon the photoconductive surface 11 after the transfer operation areremoved from the drum as it moves through cleaning station E. Here theresidual toner particles are first brought under the influsheets 14 offinal support material processed in the automatic xerographicreproducing device can be stored in the machine within a removable papercassette 18. A suitable paper cassette is set forth in U.S. patentapplication Ser. No. 208,138 filed Dec. 15, 1971.

The reproducing apparatus in accordance with this invention can alsohave the capability of accepting and processing copy sheets 14 ofvarying lengths. The length of the copy sheet 14, of course, beingdictated by the size of the original input scene or information recordedon the photconductive surface 1 1. To this end the paper cassette 18 ispreferably provided with an adjustable feature whereby sheets of varyinglength and width can be conveniently accommodated. In operation thecassette 18 is filled with a stack of final support material 19 ofpre-selected size and the cassette 18 is inserted into the machine bysliding along a base plate (now shown) which guides the cassette intooperable relationship with a pair of feed rollers 20. When properlypositioned in communication with the feed rollers 20, the top sheet ofthe stack 19 is separated and forwarded from the stack 19 into thetransfer station D by means of registration rolls 21.

It is believed that the foregoing description is sufficient for purposesof the present application to illustrate the general operation of theautomatic xerographic reproducing machine 1 which can embody theteachings of the present invention.

Referring now to FIG. 2, that portion of the reproducing machine 1 ofFIG. 1 embodying the fusing apparatus 15 of this invention is shown ingreater detail. The image bearing sheet 14 after passing through thetransfer station D of FIG. 1 upon separation from the photoconductivesurface 11 is allowed to fall into contact with a vacuum belt transportsystem 22 which conveys the sheet directly to the fusing station 1 5.

The fusing station 15 comprises a radiant type fuser. The fusing station15 comprises a heated platen 30 mounted to engage the non-image bearingside of the copy sheet 14 which moves in sliding contact therewith as itis transported through the fusing zone. The heated platen 30 is designedso that an efficient heat flow is established between the platen and thecopy sheet 14 to raise the temperature of the sheet rapidly to a levelsomewhat below the sheets scorch temperature. By controlling thetemperature of the sheet 14 in this manner the ability of the sheet toact as a heat sink during image fixing is minimized.

The radiant energy for fusing is provided by an infrared quartz lamp 3 1which is mounted in a reflector assembly 32 in opposing relationship tothe heated platen 30 and in a position to thermally communicate with theimage side of the copy sheet 14. The operating temperature of the lampis on the order of 2400K. Preferably the spectral output of the lamp 31is within a range at which the imaging material which may be toner for axerographic machine 1 is highly absorptive and at which the supportmaterial 14 which may be paper is relatively non-absorptive. As aresult, the toner images are rapidly raised to the desired fusingtemperature while the support sheet 14 remains at a relatively lowertemperature. A forced air cooling chamber 33 is provided about thebackside of the reflector assembly 32 to cool the fuser 15 in operation.

A heating element 34 is provided in the platen 30 to maintain it at thedesired temperature during standby periods. When the quartz lamp 31 isoperated the preheat element is disconnected and the platen 30 receivesits heat input directly from the quartz lamp.

The reflector assembly 32 is so constructed that it both reflects theshort wave length energy emitted from the quartz lamp 31 and absorbs thelong wave length energy with the subsequent reradiation thereof, thetemperature of the reflector being on the order of lOK. To this end thereflector 32 is a low mass construction and an air insulating barrier isprovided between the reflector and the cooling chamber 33. There-radiated long wave length energy is effective to raise thetemperature of the paper 14 to thereby assist the heating element 34 inproviding the energy necessary for fusing low density images. It will beappreciated that the reflected short wave length energy is absorbed bythe high density images to thereby effect fusing thereof.

A shield assembly 50 as best illustrated in FIG. 4 is provided topreclude physical contacting of the quartz lamp 31 and the reflector 32by the copy paper 14. The assembly 50 comprises a radiant energytransparent film 51 which has a thickness on the order of mils. Typicalmaterials which are useful as a film such as 51 are tetrafluoroethylene,flourinated ethylenepropylene and polyimide polymers. The film 51 isattached to a pair of frame or support members 52 and 53 the former ofwhich is provided with a pair of pins 54 which are received in recessesor bores 55 of the frame member 53. This arrangement allows relativemovement of the frame members by virtue of a pair of bias members in theform of coil springs 56. Temperature variations of the film will causeit to sag, consequently, the specific construction of the shieldassembly provides for a constant planar orientation of the film over theoperating temperatures of the fuser 15.

The frame members each have a flange 57 which is received in one of apair of opposed recesses 58 provided in the reflector assembly 32. Thespace between the bottoms of the recesses 58 is such as to allow forrelative movement of the frame members in a horizontal direction.

1n the modified embodiment of the fuser assembly 15, illustrated in FIG.3, the source of long wave length radiation is provided by means of aresistance heater 59 operated at a temperature on the order of l000Kwhich may be fabricated from any suitable material, for example, nicromwire.

While the invention has been described with respect to two preferredembodiments it will be apparent that certain modifications and changescan be made without departing from the spirit and the scope of theinvention and it is therefore intended that the foregoing disclosure belimited only by the claims appended hereto.

What is claimed is:

1. Apparatus for heat fusing toner images to a substrate on which theyare supported, said apparatus comprising:

a first source of radiant energy capable of emitting energy having wavelengths on the order of 0.5-2.0 microns;

a second source of radiant energy capable of emitting energy having wavelengths over 2.0 microns;

means for transporting said substrate past said sources of radiantenergy such that said toner images are directly exposed to said radiantsources;

means interposed between said radiant sources and said substrate, saidinterposed means being substantially transparent to the energy emittedfrom both of said energy sources;

said first source comprising a quartz lamp and said second sourcecomprising a resistance heating element having an operating temperaturesubstantially less than said first source; and

expansible means for mounting said means interposed between said radiantsources and said substrate in a substantially planar orientationregardless of the temperature thereof.

2. Apparatus according to claim 1, wherein said expansible means issupported by depending flanges of reflector means associated with saidenergy sources.

3. Apparatus according to claim 1, wherein said means interposed betweensaid radiant sources and said substrate comprises a shield of polyimidefilm approximately 5 mils thick.

4. Apparatus according to claim 1, wherein said means interposed betweensaid radiant sources and said substrate comprises a shield ofpolytetrafluoroethylene film on the order 5 mils in thickness.

1. Apparatus for heat fusing toner images to a substrate on which theyare supported, said apparatus comprising: a first source of radiantenergy capable of emitting energy having wave lengths on the order of0.5-2.0 microns; a second source of radiant energy capable of emittingenergy having wave lengths over 2.0 microns; means for transporting saidsubstrate past said sources of radiant energy such that said tonerimages are directly exposed to said radiant sources; means interposedbetween said radiant sources and said substrate, said interposed meansbeing substantially transparent to the energy emitted from both of saidenergy sources; said first source comprising a quartz lamp and saidsecond source comprising a resistance heating element having anoperating temperature substantially less than said first source; andexpansible means for mounting said means interposed between said radiantsources and said substrate in a substantially planar orientationregardless of the temperature thereof.
 2. Apparatus according to claim1, wherein said expansible means is supported by depending flanges ofreflector means associated with said energy sources.
 3. Apparatusaccording to claim 1, wherein said means interposed between said radiantsources and said substrate comprises a shield of polyimide filmapproximately 5 mils thick.
 4. Apparatus according to claim 1, whereinsaid means interposed between said radiant sources and said substratecomprises a shield of polytetrafluoroethylene film on the order 5 milsin thickness.